1. Field of the Invention
The present invention relates to controls for servovalves which are used for operating actuators under cyclic load conditions.
2. Prior Art
In the prior art various compensation circuits for controlling servovalves through feedback loops have been advanced. Many of these also sense a differential pressure on an actuator for providing feedback signals for different methods of control. For example U.S. Pat. Nos. 3,800,588; 3,911,732; and 3,918,298 show multiple actuator control systems which employ various types of feedback from transducers for controlling servovalves in response to load conditions at other than the controlled actuator.
Likewise, U.S. Pat. No. 3,718,033 illustrates a testing apparatus utilizing servovalve controlled actuators with a cross coupling arrangement between actuators operating along axes which are at right angles with respect to each other. This patent also discloses the use of a shaping network for providing an output signal on a nonlinear basis to its input signal for compensation.
A typical feedback loop is shown in U.S. Pat. No. 2,955,460. In relation to mechanical systems, a method of providing compensating pressures acting directly on a spool valve to attempt to maintain uniform differential pressure on the spool is disclosed in U.S. Pat. No. 3,260,273. The same type of devices are sold by Sanders Associates, Inc. Hydraulic Division, Manchester, New Hampshire, for example their Model FT10A4 and similar units which involve a type of mechanical flow control. These valves generally have quite slow responses, and are not suitable for high frequency operation in which environment most servovalves must operate for adequate testing at the present time.
Additional patents showing devices of interest include U.S. Pat. Nos. 3,488,999; 3,699,989; 3,664,358; and 2,853,667. These patents represent the state of the art uncovered in a preliminary search.